The present invention relates generally to electronic circuits, and more particularly, to power supply circuits used in electronic circuits.
Electronic circuits such as microprocessors, microcontroller units (MCUs), system-on-chips (SOCs), and application specific integrated circuits (ASICs) are used in a wide variety of applications such as industrial applications, automobiles, home appliances, and handheld devices. These circuits often operate in different power modes such as a RUN mode, a STANDBY mode, and a STOP mode. An example of a conventional electronic circuit 100 is illustrated in FIG. 1. The electronic circuit 100 includes an always ON circuit domain 102, a switchable circuit domain 104, a low power regulator 106, a power regulator 108, and a capacitor 110. The always ON circuit domain 102 receives a constant supply current from the low power regulator 106 and operates in a single mode, i.e., the RUN mode. The switchable circuit domain 104 can operate in a RUN mode and a STANDBY mode. The switchable circuit domain 104 receives a constant supply current in the RUN mode and the supply current is gated in the STANDBY mode. The STOP mode is common to both circuit domains 102, 104, in which case the power supply is shut off.
The switchable circuit domain 104 receives a supply current from a core power supply 112 in the RUN mode. The power regulator 108 is connected to the core power supply 112 and the switchable circuit domain 104 and regulates the supply current to the switchable circuit domain 104. The power regulator 108 is a high power regulator and includes a band gap voltage source 114, a buffer amplifier 116, and a switch 118, such as a p-channel metal oxide semiconductor (PMOS) transistor. The capacitor 110 is connected between the power regulator 108 and ground. The negative terminal of the buffer amplifier 116 is connected to the band gap voltage source 114 and the positive terminal of the buffer amplifier 116 is connected to a first terminal of the capacitor 110. The switch 118 is connected to the output terminal of the buffer amplifier 116, the core power supply 112 and the switchable circuit domain 104.
When the switchable circuit domain 104 transitions from the STANDBY mode to the RUN mode, the capacitor 110 must be charged to a predetermined voltage. The band gap voltage source 114 generates a voltage equivalent to this predetermined voltage (e.g., 1.2v). During the transition, the capacitor 110 is charged by the core power supply 112 and the voltage across the capacitor 110 appears at the positive terminal of the buffer amplifier 116. The initial output of the buffer amplifier 116 is about 3.3V and the switch 118, which is OFF, gates the supply current to the switchable circuit domain 104. While the capacitor 110 is charging, the buffer amplifier 116 compares the voltage across the capacitor 110 with the voltage generated by the band gap voltage source 114 and controls the ON/OFF status of the switch 118. The output of the buffer amplifier 116 gradually decreases from 3.3V to a LOW state and remains LOW as long as the voltage across the capacitor 110 is less than the voltage generated by the band gap voltage source 114. The LOW output of the buffer amplifier 116 turns the switch 118 ON and then the supply current is directed from the core power supply 112 to the switchable circuit domain 104. When the capacitor 110 is charged to the predetermined voltage, the output of the buffer amplifier 116 goes HIGH, which causes the switch 118 to enter a saturation state and thus continue conducting.
The time for the switchable circuit domain 104 to transition from the STANDBY mode to the RUN mode is known as wake-up time. The wake-up time is a function of the time taken by the capacitor 110 to be charged to the predetermined voltage. When used in automotive electronic circuits, the capacitance of the capacitor 110 can be as high as 40 microfarads (μF). The time for such a capacitor to charge to about 1.2v ranges between 400-500 microseconds. This high wake-up time degrades the performance of the electronic circuit 100.
The wake-up time can be crucial when such electronic circuits are used in time critical applications and should be as low as possible to reduce the chances of failure of the electronic circuit. One solution to reduce the wake-up time is to increase the in-rush current to the capacitor 110 (from the core power supply 112) when the switchable circuit domain 104 transitions from the RUN mode to the STANDBY mode. However, an increase in the in-rush current causes a decrease in the supply level to the switchable circuit domain 104, and decrease in supply level leads to a low voltage condition in the switchable circuit domain 104, which will trigger low voltage detectors (LVDs) and cause a system level interrupt. Such a situation is unwanted during the operation of the electronic circuit. Further, additional circuitry must be added to the electronic circuit 100 to mask the false triggering of the LVDs, which increases the size of the electronic circuit 100.
It would be advantageous to have an electronic circuit with a reduced wake-up time and that does not trigger system level interrupts.